<em>const</em> <s>x</s> = <em>true</em>
<em>const bool</em> = <b>typeof</b> <s>x</s> === <u>'boolean'</u>
<em>const bool</em> = <b>{ }.toString.call</b>(<s>x</s>) === <u>'[object Boolean]'</u>
<em>const bool</em> = <s>x</s>.<b>constructor</b> === <u>Boolean</u>
<em>const bool</em> = <q>new Boolean</q>( <s>x</s> ) <b>instanceof</b> <u>Boolean</u>